1. Field of the Invention
The invention relates to wireless data communication systems and more particularly to systems and methods for detecting node faults in access points in wireless local area networks.
2. Description of the Related Art
The use of wireless communication devices for data networking is growing at a rapid pace. Data networks that use “WiFi” (“Wireless Fidelity”) are relatively easy to install, convenient to use, and supported by the IEEE 802.11 standard. WiFi data networks also provide performance that makes WiFi a suitable alternative to a wired data network for many business and home users.
WiFi networks operate by employing wireless access points to provide users having wireless (or ‘client’) devices in proximity to the access point with access to data networks. The wireless access points contain a radio that operates according to one of three standards specified in different section of the IEEE 802.11 specification. Radios in access points communicate using omni-directional antennas in order to communicate signals with wireless devices from any direction. The access points are then connected (by hardwired connections) to a data network system that completes the users' access to the Internet.
The three standards that define the radio configurations are:                1. IEEE 802.11a, which operates on the 5 GHz band with data rates of up to 54 Mbps;        2. IEEE 802.11b, which operates on the 2.4 GHz band with data rates of up to 11 Mbps; and        3. IEEE 802.11g, which operates on the 2.4 GHz band with data rates of up to 54 Mbps.        
The 802.11b and 802.11g standards provide for some degree of interoperability. Devices that conform to 802.11b may communicate with 802.11g access points. This interoperability comes at a cost as access points will incur additional protocol overhead if any 802.11b devices are connected. Devices that conform to 802.11a may not communicate with either 802.11b or g access points. In addition, while the 802.11a standard provides for higher overall performance, 802.11a access points have a more limited range due to their operation in a higher frequency band.
Each standard defines ‘channels’ that wireless devices, or clients, use when communicating with an access point. The 802.11b and 802.11g standards each allow for 14 channels. In IEEE Std. 802.11a-1999, 200 channels are defined; each channel centered every 5 MHz from 5000 MHz to 6000 MHz. The 802.11a standard currently allows for 12 channels in the US. The 14 channels provided by 802.11b and g include only 3 channels that are not overlapping. The 12 channels provided by 802.11a are non-overlapping channels. The FCC is expected to allocate 11 additional channels in the 5.47 to 5.725 GHz band.
Some WiFi or IEEE 802.11 wireless network access points often contain multiple independently operating bi-directional radio communications nodes. Wireless access point nodes can and do fail for a variety of reasons as diverse as random ionizing radiation disrupting an electronic component, timing or race conditions in the tens of thousands of lines of software and programmable hardware code, and actual component failure due to ageing, thermal cycling, or manufacturing tolerance or error. One advantage of multi-radio access points is that they provide fault tolerant communication between the access point and its associated clients. When one or more radios fail, the remaining radios can continue to provide communications service to the clients associated with the access point.
In order to reduce system degradation, there is a need to reliably identify failed nodes and reactivate or replace them. Present methods of determining failure rely on monitoring data communications between the access points and their clients and reporting the presence or absence of transferred data. However, access point clients typically operate in a relatively autonomous manner when choosing a particular access point node with which to associate. For this reason a lack of associated clients may not, by itself, be a reliable method of failure identification.
There is a need for systems and methods that more reliably identify failed nodes, and to reactivate or replace them.